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Non-Perturbative QCD at Finite Temperature
Pok Man Lo
University of Pittsburgh
Jlab Hugs student talk, 6-20-2008
Pok Man Lo (UPitt) Non-Perturbative QCD at finite Temperature 6-20-2008 1 / 39
personal information
email: [email protected]
institution: University of Pittsburgh
advisor: Eric Swanson
Pok Man Lo (UPitt) Non-Perturbative QCD at finite Temperature 6-20-2008 2 / 39
outline
1 Non-perturbative QCD at zero temperatureIntroduction to non-perturbative physicsTools for studying non-perturbative QCD
DiagrammaticsSchwinger Dyson Equation
Illustration: Gap Equation Revisited
2 Finite Temperature Field TheorySurvey of basic formalism of Finite Temperature of Field TheoryFinite Temperature Gap Equation
Pok Man Lo (UPitt) Non-Perturbative QCD at finite Temperature 6-20-2008 3 / 39
Outline
1 Non-perturbative QCD at zero temperatureIntroduction to non-perturbative physicsTools for studying non-perturbative QCD
DiagrammaticsSchwinger Dyson Equation
Illustration: Gap Equation Revisited
2 Finite Temperature Field TheorySurvey of basic formalism of Finite Temperature of Field TheoryFinite Temperature Gap Equation
Pok Man Lo (UPitt) Non-Perturbative QCD at finite Temperature 6-20-2008 4 / 39
Introduction
The progress of theoretical physics
The search for exact solution:
Newtonian physics: 3-body problem was insoluble
QED: 2-body and 1-body problem was insoluble
now: 0-body, namely, the vacuum is insoluble
No body is too many!!
Pok Man Lo (UPitt) Non-Perturbative QCD at finite Temperature 6-20-2008 5 / 39
Introduction
The progress of theoretical physics
The search for exact solution:
Newtonian physics: 3-body problem was insoluble
QED: 2-body and 1-body problem was insoluble
now: 0-body, namely, the vacuum is insoluble
No body is too many!!
Pok Man Lo (UPitt) Non-Perturbative QCD at finite Temperature 6-20-2008 5 / 39
Introduction
The progress of theoretical physics
The search for exact solution:
Newtonian physics: 3-body problem was insoluble
QED: 2-body and 1-body problem was insoluble
now: 0-body, namely, the vacuum is insoluble
No body is too many!!
Pok Man Lo (UPitt) Non-Perturbative QCD at finite Temperature 6-20-2008 5 / 39
Introduction
The progress of theoretical physics
The search for exact solution:
Newtonian physics: 3-body problem was insoluble
QED: 2-body and 1-body problem was insoluble
now: 0-body, namely, the vacuum is insoluble
No body is too many!!
Pok Man Lo (UPitt) Non-Perturbative QCD at finite Temperature 6-20-2008 5 / 39
Introduction
The progress of theoretical physics
The search for exact solution:
Newtonian physics: 3-body problem was insoluble
QED: 2-body and 1-body problem was insoluble
now: 0-body, namely, the vacuum is insoluble
No body is too many!!
Pok Man Lo (UPitt) Non-Perturbative QCD at finite Temperature 6-20-2008 5 / 39
Introduction
The progress of theoretical physics
The search for exact solution:
Newtonian physics: 3-body problem was insoluble
QED: 2-body and 1-body problem was insoluble
now: 0-body, namely, the vacuum is insoluble
No body is too many!!
Pok Man Lo (UPitt) Non-Perturbative QCD at finite Temperature 6-20-2008 5 / 39
Introduction
Difficutly in calculating arbitarily complicated diagram
Impossible to sum all the diagrams
Pok Man Lo (UPitt) Non-Perturbative QCD at finite Temperature 6-20-2008 6 / 39
Introduction
Difficutly in calculating arbitarily complicated diagram
Impossible to sum all the diagrams
Pok Man Lo (UPitt) Non-Perturbative QCD at finite Temperature 6-20-2008 6 / 39
Introduction
Perturbation: expansion in α
is not useful if α is not small
cannot explain non-perturbative phenomena:e.g bound state formation and spontaneous symmetry breaking
classical mechanics example: mass attached to a spring: A sin(√
km t)
Pok Man Lo (UPitt) Non-Perturbative QCD at finite Temperature 6-20-2008 7 / 39
Introduction
Perturbation: expansion in α
is not useful if α is not small
cannot explain non-perturbative phenomena:e.g bound state formation and spontaneous symmetry breaking
classical mechanics example: mass attached to a spring: A sin(√
km t)
Pok Man Lo (UPitt) Non-Perturbative QCD at finite Temperature 6-20-2008 7 / 39
Introduction
Perturbation: expansion in α
is not useful if α is not small
cannot explain non-perturbative phenomena:e.g bound state formation and spontaneous symmetry breaking
classical mechanics example: mass attached to a spring: A sin(√
km t)
Pok Man Lo (UPitt) Non-Perturbative QCD at finite Temperature 6-20-2008 7 / 39
Introduction
Perturbation: expansion in α
is not useful if α is not small
cannot explain non-perturbative phenomena:e.g bound state formation and spontaneous symmetry breaking
classical mechanics example: mass attached to a spring: A sin(√
km t)
Pok Man Lo (UPitt) Non-Perturbative QCD at finite Temperature 6-20-2008 7 / 39
Outline
1 Non-perturbative QCD at zero temperatureIntroduction to non-perturbative physicsTools for studying non-perturbative QCD
DiagrammaticsSchwinger Dyson Equation
Illustration: Gap Equation Revisited
2 Finite Temperature Field TheorySurvey of basic formalism of Finite Temperature of Field TheoryFinite Temperature Gap Equation
Pok Man Lo (UPitt) Non-Perturbative QCD at finite Temperature 6-20-2008 8 / 39
illustration of the failure of perturbation
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 2 4 6 8 10
...an innocent looking function
using Taylor expansion, we write
f (x) = A0 + A1x + A2x2 + ...
A0,A1,A2, ... are all strightly 0!
Pok Man Lo (UPitt) Non-Perturbative QCD at finite Temperature 6-20-2008 9 / 39
illustration of the failure of perturbation
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 2 4 6 8 10
...an innocent looking functionusing Taylor expansion, we write
f (x) = A0 + A1x + A2x2 + ...
A0,A1,A2, ... are all strightly 0!
Pok Man Lo (UPitt) Non-Perturbative QCD at finite Temperature 6-20-2008 9 / 39
illustration of the failure of perturbation
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 2 4 6 8 10
...an innocent looking functionusing Taylor expansion, we write
f (x) = A0 + A1x + A2x2 + ...
A0,A1,A2, ... are all strightly 0!
Pok Man Lo (UPitt) Non-Perturbative QCD at finite Temperature 6-20-2008 9 / 39
illustration of the failure of perturbation
differential equation...
f (x) + x3f ′ = 0
f (x) = exp−1x2
any other method will work, other than perturbation!
Pok Man Lo (UPitt) Non-Perturbative QCD at finite Temperature 6-20-2008 10 / 39
illustration of the failure of perturbation
differential equation...
f (x) + x3f ′ = 0
f (x) = exp−1x2
any other method will work, other than perturbation!
Pok Man Lo (UPitt) Non-Perturbative QCD at finite Temperature 6-20-2008 10 / 39
illustration of the failure of perturbation
differential equation...
f (x) + x3f ′ = 0
f (x) = exp−1x2
any other method will work, other than perturbation!
Pok Man Lo (UPitt) Non-Perturbative QCD at finite Temperature 6-20-2008 10 / 39
illustration of the failure of perturbation
differential equation...
f (x) + x3f ′ = 0
f (x) = exp−1x2
any other method will work, other than perturbation!
Pok Man Lo (UPitt) Non-Perturbative QCD at finite Temperature 6-20-2008 10 / 39
Different Philosophy
Perturbative Vs Non-perturbative:
perturbative method: sum all diagrams up to certain order in α
non-perturbative method: sum a certain class of diagram to all order
in some sense, non-perturbative method includes the whole perturbationmethod as the latter is just a classification of diagram by the couplingconstant αapproximation 6= perturbation!QFT contains more than just the S-matrix and perturbation!
Pok Man Lo (UPitt) Non-Perturbative QCD at finite Temperature 6-20-2008 11 / 39
Different Philosophy
Perturbative Vs Non-perturbative:
perturbative method: sum all diagrams up to certain order in α
non-perturbative method: sum a certain class of diagram to all order
in some sense, non-perturbative method includes the whole perturbationmethod as the latter is just a classification of diagram by the couplingconstant αapproximation 6= perturbation!QFT contains more than just the S-matrix and perturbation!
Pok Man Lo (UPitt) Non-Perturbative QCD at finite Temperature 6-20-2008 11 / 39
Different Philosophy
Perturbative Vs Non-perturbative:
perturbative method: sum all diagrams up to certain order in α
non-perturbative method: sum a certain class of diagram to all order
in some sense, non-perturbative method includes the whole perturbationmethod as the latter is just a classification of diagram by the couplingconstant αapproximation 6= perturbation!QFT contains more than just the S-matrix and perturbation!
Pok Man Lo (UPitt) Non-Perturbative QCD at finite Temperature 6-20-2008 11 / 39
Different Philosophy
Perturbative Vs Non-perturbative:
perturbative method: sum all diagrams up to certain order in α
non-perturbative method: sum a certain class of diagram to all order
in some sense, non-perturbative method includes the whole perturbationmethod as the latter is just a classification of diagram by the couplingconstant α
approximation 6= perturbation!QFT contains more than just the S-matrix and perturbation!
Pok Man Lo (UPitt) Non-Perturbative QCD at finite Temperature 6-20-2008 11 / 39
Different Philosophy
Perturbative Vs Non-perturbative:
perturbative method: sum all diagrams up to certain order in α
non-perturbative method: sum a certain class of diagram to all order
in some sense, non-perturbative method includes the whole perturbationmethod as the latter is just a classification of diagram by the couplingconstant αapproximation 6= perturbation!
QFT contains more than just the S-matrix and perturbation!
Pok Man Lo (UPitt) Non-Perturbative QCD at finite Temperature 6-20-2008 11 / 39
Different Philosophy
Perturbative Vs Non-perturbative:
perturbative method: sum all diagrams up to certain order in α
non-perturbative method: sum a certain class of diagram to all order
in some sense, non-perturbative method includes the whole perturbationmethod as the latter is just a classification of diagram by the couplingconstant αapproximation 6= perturbation!QFT contains more than just the S-matrix and perturbation!
Pok Man Lo (UPitt) Non-Perturbative QCD at finite Temperature 6-20-2008 11 / 39
Outline
1 Non-perturbative QCD at zero temperatureIntroduction to non-perturbative physicsTools for studying non-perturbative QCD
DiagrammaticsSchwinger Dyson Equation
Illustration: Gap Equation Revisited
2 Finite Temperature Field TheorySurvey of basic formalism of Finite Temperature of Field TheoryFinite Temperature Gap Equation
Pok Man Lo (UPitt) Non-Perturbative QCD at finite Temperature 6-20-2008 12 / 39
motivation
perturbation does not help as we want to sum diagrams to all order in α
new tools other than perturbation!
in some sense, we need exact relations among diagrams!
two particularly useful ones:
Diagrammatics
Schwinger Dyson Equation
Pok Man Lo (UPitt) Non-Perturbative QCD at finite Temperature 6-20-2008 13 / 39
method of partial sum
summing a particular class of diagrams to all order
to be explicit, let’s consider the diagrams for constructing a propagator
Pok Man Lo (UPitt) Non-Perturbative QCD at finite Temperature 6-20-2008 14 / 39
method of partial sum
summing a particular class of diagrams to all order
to be explicit, let’s consider the diagrams for constructing a propagator
Pok Man Lo (UPitt) Non-Perturbative QCD at finite Temperature 6-20-2008 14 / 39
diagrammatics of propagator
in general, to construct the propagator, we need to sum...
Pok Man Lo (UPitt) Non-Perturbative QCD at finite Temperature 6-20-2008 15 / 39
diagrammatics of propagator
in general, we cannot sum them all!
but let’s focus on the following class of diagram:
Pok Man Lo (UPitt) Non-Perturbative QCD at finite Temperature 6-20-2008 16 / 39
diagrammatics of propagator
in general, we cannot sum them all!
but let’s focus on the following class of diagram:
Pok Man Lo (UPitt) Non-Perturbative QCD at finite Temperature 6-20-2008 16 / 39
diagrammatics of propagator
in general, we cannot sum them all!
but let’s focus on the following class of diagram:
Pok Man Lo (UPitt) Non-Perturbative QCD at finite Temperature 6-20-2008 17 / 39
diagrammatics of propagator
the above procedure should be compared with the summing of geometricseries:
1
1− x= 1 + x + x2 + x3 + ...
Pok Man Lo (UPitt) Non-Perturbative QCD at finite Temperature 6-20-2008 18 / 39
diagrammatics of propagator
Two comments:
inspired by the series, we know we can do better:
Pok Man Lo (UPitt) Non-Perturbative QCD at finite Temperature 6-20-2008 19 / 39
diagrammatics of propagator
Two comments:
inspired by the series, we know we can do better:
Pok Man Lo (UPitt) Non-Perturbative QCD at finite Temperature 6-20-2008 19 / 39
diagrammatics of propagator
Two comments:
inspired by the series, we know we can do better:
Pok Man Lo (UPitt) Non-Perturbative QCD at finite Temperature 6-20-2008 19 / 39
diagrammatics of propagator
⇐⇒ 6p −m
Pok Man Lo (UPitt) Non-Perturbative QCD at finite Temperature 6-20-2008 20 / 39
diagrammatics of propagator
⇐⇒ 6p −m
Pok Man Lo (UPitt) Non-Perturbative QCD at finite Temperature 6-20-2008 20 / 39
diagrammatics of propagator
⇐⇒ dynamical mass
Pok Man Lo (UPitt) Non-Perturbative QCD at finite Temperature 6-20-2008 21 / 39
diagrammatics of propagator
⇐⇒ dynamical mass
Pok Man Lo (UPitt) Non-Perturbative QCD at finite Temperature 6-20-2008 21 / 39
Schwinger Dyson Equation
an exact relations among n-point functions
basic idea: ∫dx
d
dxf (x)− > 0
Z =
∫DψDψDGe i(S+
Rηψ+ψη+...)/
∫DψDψDGe i(S)
using the fact ∫DψDψDG (
δ
δψe i(S+
Rηψ+ψη+...)) = 0
Z = e iW
Pok Man Lo (UPitt) Non-Perturbative QCD at finite Temperature 6-20-2008 22 / 39
Schwinger Dyson Equation
an exact relations among n-point functions
basic idea: ∫dx
d
dxf (x)− > 0
Z =
∫DψDψDGe i(S+
Rηψ+ψη+...)/
∫DψDψDGe i(S)
using the fact ∫DψDψDG (
δ
δψe i(S+
Rηψ+ψη+...)) = 0
Z = e iW
Pok Man Lo (UPitt) Non-Perturbative QCD at finite Temperature 6-20-2008 22 / 39
Schwinger Dyson Equation
an exact relations among n-point functions
basic idea: ∫dx
d
dxf (x)− > 0
Z =
∫DψDψDGe i(S+
Rηψ+ψη+...)/
∫DψDψDGe i(S)
using the fact ∫DψDψDG (
δ
δψe i(S+
Rηψ+ψη+...)) = 0
Z = e iW
Pok Man Lo (UPitt) Non-Perturbative QCD at finite Temperature 6-20-2008 22 / 39
Schwinger Dyson Equation
an exact relations among n-point functions
basic idea: ∫dx
d
dxf (x)− > 0
Z =
∫DψDψDGe i(S+
Rηψ+ψη+...)/
∫DψDψDGe i(S)
using the fact ∫DψDψDG (
δ
δψe i(S+
Rηψ+ψη+...)) = 0
Z = e iW
Pok Man Lo (UPitt) Non-Perturbative QCD at finite Temperature 6-20-2008 22 / 39
Schwinger Dyson Equation
as an illustration, for the Hamiltonian:
H =
∫d3xψ†~xγ
0[−i~γ · ∇+ m]ψ~x − G
∫d3xd3yV~x~yψ
†~xT
aψ~xψ†~yT aψ~y
Schwinger Dyson Equation
(iγ · ∂x −m)δ2Wδηxδηy
+ 2G
∫d4zV γ0T ai
δ2Wδηxδηz
γ0T a δ2Wδηzδηy
= δxy
Pok Man Lo (UPitt) Non-Perturbative QCD at finite Temperature 6-20-2008 23 / 39
Outline
1 Non-perturbative QCD at zero temperatureIntroduction to non-perturbative physicsTools for studying non-perturbative QCD
DiagrammaticsSchwinger Dyson Equation
Illustration: Gap Equation Revisited
2 Finite Temperature Field TheorySurvey of basic formalism of Finite Temperature of Field TheoryFinite Temperature Gap Equation
Pok Man Lo (UPitt) Non-Perturbative QCD at finite Temperature 6-20-2008 24 / 39
Gap Equation Revisited
to illustrate the main idea above, we look at the gap equation
consider the Hamiltonian:
H =
∫d3xψ†~xγ
0[−i~γ · ∇+ m]ψ~x − G
∫d3xd3yV~x~yψ
†~xT
aψ~xψ†~yT aψ~y
for the contact case: V → δ(3)
this corresonds to the case where the quark exchange an instantaneousgluon locally
Pok Man Lo (UPitt) Non-Perturbative QCD at finite Temperature 6-20-2008 25 / 39
Gap Equation Revisited
to illustrate the main idea above, we look at the gap equation
consider the Hamiltonian:
H =
∫d3xψ†~xγ
0[−i~γ · ∇+ m]ψ~x − G
∫d3xd3yV~x~yψ
†~xT
aψ~xψ†~yT aψ~y
for the contact case: V → δ(3)
this corresonds to the case where the quark exchange an instantaneousgluon locally
Pok Man Lo (UPitt) Non-Perturbative QCD at finite Temperature 6-20-2008 25 / 39
Gap Equation Revisited
the gap equation tell you how the quark is dressed according to theHamiltonian
namely, the dynamical mass generated:
before showing you the answer, we need to perform our final dressing...
Pok Man Lo (UPitt) Non-Perturbative QCD at finite Temperature 6-20-2008 26 / 39
the final dressing
in fact we miss some diagram...
Pok Man Lo (UPitt) Non-Perturbative QCD at finite Temperature 6-20-2008 27 / 39
the final dressing
Pok Man Lo (UPitt) Non-Perturbative QCD at finite Temperature 6-20-2008 28 / 39
the final dressing
Pok Man Lo (UPitt) Non-Perturbative QCD at finite Temperature 6-20-2008 29 / 39
Gap Equation Revisited
the gap equation for the general case:
Generalized Gap Equation
M(~k) = m − GTr [TT ]
Nc
∫d3k ′
(2π)3V~k ′−~k [
M(~k ′)
E~k ′− k̂ ′ · k̂ |
~k ′|M(~k)
E~k ′ |~k|]
M(~k) in general is a function of ~k
it dictates how the mass is dynamically generated
Pok Man Lo (UPitt) Non-Perturbative QCD at finite Temperature 6-20-2008 30 / 39
Gap Equation Revisitedfor the contact case, we have...
0
0.5
1
1.5
2
2.5
3
3.5
4
0 0.5 1 1.5 2 2.5 3 3.5 4
M
current mass m
Dynamical Mass Generation
|G| > G_critical|G| < G_critical
Pok Man Lo (UPitt) Non-Perturbative QCD at finite Temperature 6-20-2008 31 / 39
Outline
1 Non-perturbative QCD at zero temperatureIntroduction to non-perturbative physicsTools for studying non-perturbative QCD
DiagrammaticsSchwinger Dyson Equation
Illustration: Gap Equation Revisited
2 Finite Temperature Field TheorySurvey of basic formalism of Finite Temperature of Field TheoryFinite Temperature Gap Equation
Pok Man Lo (UPitt) Non-Perturbative QCD at finite Temperature 6-20-2008 32 / 39
motivation
FTFT is needed to study the physics of QGP, deconfinement and chiralrestoration
when calculating observables in QFT, we only calculate the vacuumexpectation value
at finite temperature, excited states start to contribute, the interestingquantity should be the thermal average of the observables
we expect nE~kto enter QFT
partition function dictates the equilibrium Finite Temperature QFT
Pok Man Lo (UPitt) Non-Perturbative QCD at finite Temperature 6-20-2008 33 / 39
Outline
1 Non-perturbative QCD at zero temperatureIntroduction to non-perturbative physicsTools for studying non-perturbative QCD
DiagrammaticsSchwinger Dyson Equation
Illustration: Gap Equation Revisited
2 Finite Temperature Field TheorySurvey of basic formalism of Finite Temperature of Field TheoryFinite Temperature Gap Equation
Pok Man Lo (UPitt) Non-Perturbative QCD at finite Temperature 6-20-2008 34 / 39
basics of FTFTthe partition function:
Z = Tr [e−βH ] =
∫dq < q|e−βH |q >
observables are given by
O = Tr [e−βHO] =<< q|O|q >working in imaginary time τ = it
a corresponding path integral representation of the partition function, withPeriodic/Antiperiodic boundary condition
the boundary condition motivates the use of Matsubara Green’s function:
∫dk0 → 1
βΣωn
Pok Man Lo (UPitt) Non-Perturbative QCD at finite Temperature 6-20-2008 35 / 39
Outline
1 Non-perturbative QCD at zero temperatureIntroduction to non-perturbative physicsTools for studying non-perturbative QCD
DiagrammaticsSchwinger Dyson Equation
Illustration: Gap Equation Revisited
2 Finite Temperature Field TheorySurvey of basic formalism of Finite Temperature of Field TheoryFinite Temperature Gap Equation
Pok Man Lo (UPitt) Non-Perturbative QCD at finite Temperature 6-20-2008 36 / 39
Gap equation in Finite Temperature
Generalized Gap Equation
M(~k) = m− GTr [TT ]
Nc
∫d3k ′
(2π)3V~k ′−~k [
M(~k ′)
E~k ′− k̂ ′ · k̂ |
~k ′|M(~k)
E~k ′ |~k |](1− 2nE~k′
)
with nE~k= 1
eβE~k +1
Pok Man Lo (UPitt) Non-Perturbative QCD at finite Temperature 6-20-2008 37 / 39
summary
non-perturbative physics with e−1x2
summation of a class of diagram with 11−x
Schwinger Dyson Equation with∫
dx ddx f (x)
Finite Temperature Field Theory with Tr [e−βH ]
Pok Man Lo (UPitt) Non-Perturbative QCD at finite Temperature 6-20-2008 38 / 39
thank you
Pok Man Lo (UPitt) Non-Perturbative QCD at finite Temperature 6-20-2008 39 / 39